Known internal combustion engines have cylinders in which a gaseous mixture of fuel and air is burnt in order to generate torque. The quantity of mixture admitted into a cylinder prior to ignition is decisive with regard to the torque delivered by said cylinder. To enable the torque delivered by the internal combustion engine to be adapted to different loads, known internal combustion engines have throttle valves which reduce the admission of mixture into the cylinders in a controllable way. However, the use of throttle valves is linked to throttle losses stemming from the resistance to flow which throttle valves cause.
To prevent throttle losses it is known for the quantity of gas flowing into a cylinder to be regulated by means of a valve stroke. Depending on the desired quantity of mixture to be admitted to the cylinder, one or more inlet valves on the cylinder are opened to a greater or lesser extent. This solution offers improved efficiency due to the reduction in throttle loss. The inlet valves can be opened mechanically, electromechanically or electrically. For example the inlet valves can be mechanically actuated by means of an adjustable intermediate mechanism that uses a camshaft.
In the prior art the valves of some or all of the cylinders are actuated by a common camshaft. Then the same valve stroke is set for each cylinder and consequently every cylinder receives an identical amount of mixture. In practice, though, tolerances arising during manufacture and in the components themselves lead to a variation in the resulting valve stroke and therefore also to a variation in the amount of mixture per cylinder. As a consequence the individual cylinders deliver different amounts of torque. When the valve strokes are small these differences have a particularly strong effect, since the percentage deviation is at its greatest in these conditions. Differences in the filling and torque amounts between the individual cylinders lead not only to increased rough running in the internal combustion engine but also to variations in the mixture attended by a worsening of exhaust gas quality together with increased engine wear.
Since the effects of manufacturing and component tolerances are particularly serious when the valve stroke settings are small, it is known in the prior art for a value to be established for a minimum valve stroke which guarantees an acceptable torque deviation in the different cylinders and which the valve stroke must not fall below. This value is empirically determined according to the prior art for a series of internal combustion engines and then permanently specified for every exemplar of the series. The chosen value is large enough to ensure that all exemplars in the series provide satisfactory running despite manufacturing and component tolerances.
However, due to this necessarily quite large minimum valve stroke value it is not possible to decrease the power of the internal combustion engine by reducing the valve stroke, and this effect must therefore be reproduced by using the throttle valve. This in turn gives rise to the throttle losses already described.